JDBC: Part I

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JDBC Part I
2
Attribution

• These slides are based on three primary sources
• Sun JDBC Tutorial
• URL http//java.sun.com/docs/books/tutorial/
  jdbc/TOC.html
• George Reese, Database Programming with JDBC and
  Java (OReilly Associates.)
• Marty Hall, Core Web Programming (Prentice
  Hall.)

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Road Map

• Introduction to JDBC/JDBC Drivers
• Overview Six Steps to using JDBC
• Example 1 Setting up Tables via JDBC
• Example 2 Inserting Data via JDBC
• Example 3 Querying Data via JDBC
• Exception Handling Overview

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Introduction to JDBC andJDBC Drivers
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Introduction to JDBC

• JDBC is a simple API for connecting from Java
  applications to multiple databases.
• Lets you smoothly translate between the world of
  the database, and the world of the Java
  application.
• The idea of a universal database access API is
  not a new one.
• For example, Open Database Connectivity (ODBC)
  was developed to create a single standard for
  database access in the Windows environment.
• JDBC API aims to be as simple as possible while
  providing developers with maximum flexibility.

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Understanding JDBC Drivers

• To connect to a database
• , you first need a JDBC Driver.
• JDBC Driver
• set of classes that interface with a specific
  database engine.

Java Application
JDBC Driver Manager
JDBC- ODBC Bridge
Vendor Specific JDBC Driver
Vendor Specific JDBC Driver
Database
Database
Diagram Source Marty Hall, Core Web
Programming (Prentice Hall.)
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JDBC Drivers

• JDBC drivers exist for every major database
  including
• Oracle, SQL Server, Sybase, and MySQL.
• For MySQL,
• we will be using the open source MySQL
  Connector/J.
• http//www.mysql.com/downloads/api-jdbc.html.

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Installing the MySQL Driver

• To use the MySQL Connector/J Driver,
• you need to download the complete distribution
• and
• Add the following JAR to your CLASSPATH (change
  version with the actual version of connector you
  downloaded such as 3.1.7
• mysql-connector-java-version-stable-bin.jar
• To use the driver within Tomcat, copy the jar
  file above to
• TOMCAT_HOME\ROOT\WEB-INF\lib

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Overview Six Steps to Using JDBC
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Six Steps to Using JDBC

• Load the JDBC Driver
• Establish the Database Connection
• Create a Statement Object
• Execute a Query
• Process the Results
• Close the Connection

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1) Loading the JDBC Driver

• To use a JDBC driver,
• you must load the driver via the Class.forName()
  method.
• In general, the code looks like this
• Class.forName("jdbc.DriverXYZ")
• where jbdc.DriverXYZ is the JDBC Driver you want
  to load.
• To use MySQL and load jdbc driver
• Class.forName(com.mysql.odbc.driver")
• To use ORACLE and load jdbc driver
• Class.forName(oracle.odbc.driver.OracleDriver")
• If you are using SUN JDBC-ODBC Driver, your code
  will look like this
• Class.forName("sun.jdbc.odbc.JdbcOdbcDriver")

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Loading the MySQL Driver Class.forName("com.mysql
.jdbc.Driver")//use the above with project 5 to
load driver

• If you are using the MM MySQL Driver, your code
  will look like this
• try
• Class.forName("com.mysql.jdbc.Driver")
• catch(java.lang.ClassNotFoundException e)
• System.err.print("ClassNotFoundException
  ")
• System.err.println(e.getMessage())
• Class.forName() will
• throw a ClassNotFoundException if your CLASSPATH
  is not set up properly.
• Hence, it's a good idea to surround the forName()
  with a try/catch block.

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2) Establish the Connection

• Once you have loaded your JDBC driver,
• the next step is to establish a database
  connection.
• The following line of code illustrates the basic
  idea
• Connection con DriverManager.getConnection(url)

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Creating a Connection URL

• The only difficulty in establishing a connection
  is specifying the correct URL.
• In general, the URL has the following format
  jdbcsubprotocolsubname.
• JDBC indicates that this is a JDBC Connection (no
  mystery there!)
• The subprotocol identifies the driver you want to
  use.
• The subname identifies the database
  name/location.

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Connection URL ODBC

• For example, the following code uses a
• JDBC-ODBC bridge to connect to the local Fred
  database
• String url "jdbcodbcFred"
• Connection con DriverManager.getConnection(url,
  username", "password")

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Connection URL MySQLuse this with project5

• Here's how you might connect to MySQL
• String url
• "jdbcmysql//localhost/databasename"
• Connection con DriverManager.getConnection(u
  rl)
• In this case,
• we are using the MySQL JDBC Driver
• to connect to the databasebasename,
• located on the localhost machine.
• If this code executes successfully, we will have
  a Connection object for communicating directly
  with the database.

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3) Create a Statement Object

• The JDBC Statement object sends SQL statements to
  the database.
• Statement objects are created from active
  Connection objects.
• For example
• Statement stmt con.createStatement()
• With a Statement object, you can issue SQL calls
  directly to the database.

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4) Execute a Query

• executeQuery()
• Executes the SQL query and returns the data in a
  table (ResultSet)
• The resulting table may be empty but never null
• ResultSet results
• statement.executeQuery("SELECT a, b FROM
  table")
• executeUpdate()
• Used to execute for INSERT, UPDATE, or DELETE SQL
  statements
• The return is the number of rows that were
  affected in the database
• Supports Data Definition Language (DDL)
  statements CREATE TABLE, DROP TABLE and ALTER
  TABLE

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Useful Statement Methods

• getMaxRows/setMaxRows
• Determines the number of rows a ResultSet may
  contain
• Unless explicitly set, the number of rows are
  unlimited (return value of 0)
• getQueryTimeout/setQueryTimeout
• Specifies the amount of a time a driver will wait
  for a
• STATEMENT to complete before throwing a
• SQLException

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5) Process the Results

• A ResultSet contains the results of the SQL
  query.
• Useful Methods
• All methods can throw a SQLException
• close
• Releases the JDBC and database resources
• The result set is automatically closed when the
  associated Statement object executes a new query
• getMetaDataObject
• Returns a ResultSetMetaData object containing
  information about the columns in the ResultSet

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ResultSet (Continued)

• Useful Methods
• next
• Attempts to move to the next row in the ResultSet
• If successful true is returned
• otherwise, false
• The first call to next positions the cursor a the
  first row

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ResultSet (Continued)

• Useful Methods
• findColumn
• Returns the corresponding integer value
  corresponding to the specified column name
• Column numbers in the result set do not
  necessarily map to the same column numbers in the
  database
• getXxx
• Returns the value from the column specified by
  column name or column index as an Xxx Java type
• Returns 0 or null, if the value is a SQL NULL
• Legal getXxx types

double byte int Date String float short
long Time Object
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6) Close the Connection

• To close the database connection
• stmt.close()
• connection.close()
• Note Some application servers, such as BEA
  WebLogic maintain a pool of database connections.
• This is much more efficient, as applications do
  not have the overhead of constantly opening and
  closing database connections.

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Example 1Setting Up Tables via JDBC
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The Coffee Tables

• To get started, we will first examine JDBC code
  for creating new tables.
• This java code creates a table for storing coffee
  data
• Heres the SQL Statement
• CREATE TABLE COFFEES
• (COF_NAME VARCHAR(32),
• SUP_ID INTEGER,
• PRICE FLOAT,
• SALES INTEGER,
• TOTAL INTEGER)

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The Coffees Tables
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The Coffee Table

• You could create this table via MySQL, but you
  can also create it via JDBC.
• A few things to note about the table
• The column named SUP_ID contains an integer value
  indicating a Supplier ID.
• Suppliers will be stored in a separate table.
• In this case, SUP_ID is referred to as a foreign
  key.
• The column named SALES stores values of SQL type
  INTEGER and indicates the number of pounds of
  coffee sold during the current week.
• The final column, TOTAL, contains a SQL INTEGER
  which gives the total number of pounds of coffee
  sold to date.

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import java.sql. public class CreateCoffees
public static void main(String args)
String url "jdbcmysql//localhost/coffee"
Connection con String
createString createString "create
table COFFEES "
"(COF_NAME VARCHAR(32), "
"SUP_ID INTEGER, "
"PRICE FLOAT, "
"SALES INTEGER, "
"TOTAL INTEGER)" Statement stmt
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try Class.forName("com.mysql
.jdbc.Driver") catch(java.lang.ClassNot
FoundException e)
System.err.print("ClassNotFoundException ")
System.err.println(e.getMessage())
try con
DriverManager.getConnection(url)
stmt con.createStatement()
stmt.executeUpdate(createString)
stmt.close() con.close()
catch(SQLException ex)
System.err.println("SQLException "
ex.getMessage())
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Example 2Inserting Data via JDBC
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import java.sql. public class InsertCoffees
public static void main(String args)
throws SQLException
System.out.println ("Adding Coffee Data")
ResultSet rs null
PreparedStatement ps null
String url "jdbcmysql//localhost/coffee"
Connection con
Statement stmt try
Class.forName("com.mysql.jdbc.Driver")
catch(java.lang.ClassNotFoundE
xception e)
System.err.print("ClassNotFoundException ")
System.err.println(e.getMessag
e())
1
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try con
DriverManager.getConnection(url)
stmt con.createStatement()
stmt.executeUpdate ("INSERT INTO
COFFEES "
"VALUES('Amaretto', 49, 9.99, 0, 0)")
stmt.executeUpdate ("INSERT INTO
COFFEES "
"VALUES('Hazelnut', 49, 9.99, 0, 0)")
stmt.executeUpdate ("INSERT INTO
COFFEES "
"VALUES('Amaretto_decaf', 49, 10.99, 0, 0)")
stmt.executeUpdate ("INSERT
INTO COFFEES "
"VALUES('Hazelnut_decaf', 49, 10.99, 0, 0)")
stmt.close()
con.close()
System.out.println ("Done")
catch(SQLException ex)
System.err.println("-----SQLException-----")
System.err.println("SQLState
" ex.getSQLState())
System.err.println("Message "
ex.getMessage())
System.err.println("Vendor "
ex.getErrorCode())
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Example 3Querying Data via JDBC
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import java.sql. public class SelectCoffees
public static void main(String args)
throws SQLException ResultSet
rs null PreparedStatement ps
null String url
"jdbcmysql//localhost/coffee"
Connection con Statement stmt
try Class.forName("com.mys
ql.jdbc.Driver")
catch(java.lang.ClassNotFoundException e)
System.err.print("ClassNotFoundE
xception ")
System.err.println(e.getMessage())
try con
DriverManager.getConnection(url)
stmt con.createStatement()
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4
ResultSet uprs stmt.executeQuery("SELEC
T FROM COFFEES")
System.out.println("Table COFFEES")
while (uprs.next())
String name uprs.getString("COF_
NAME") int id
uprs.getInt("SUP_ID")
float price uprs.getFloat("PRICE")
int sales
uprs.getInt("SALES")
int total uprs.getInt("TOTAL")
System.out.print(name " "
id " " price)
System.out.println(" " sales " "
total)
uprs.close()
stmt.close()
con.close()
catch(SQLException ex)
System.err.println("-----SQLException-----")
System.err.println("SQLState
" ex.getSQLState())
System.err.println("Message "
ex.getMessage())
System.err.println("Vendor "
ex.getErrorCode())
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JDBC Exception Handling
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Exception Handling

• SQL Exceptions
• Nearly every JDBC method can throw a SQLException
  in response to a data access error
• If more than one error occurs, they are chained
  together
• SQL exceptions contain
• Description of the error, getMessage
• The SQLState (Open Group SQL specification)
  identifying the exception, getSQLState
• A vendor-specific integer, error code,
  getErrorCode
• A chain to the next SQLException,
  getNextException

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SQL Exception Example

• try
• ... // JDBC statement.
• catch (SQLException sqle)
• while (sqle ! null)
• System.out.println("Message "
  sqle.getMessage())
• System.out.println("SQLState "
  sqle.getSQLState())
• System.out.println("Vendor Error "
• sqle.getErrorCode())
• sqle.printStrackTrace(System.out)
• sqle sqle.getNextException()

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Summary

• The JDBC Driver connections a Java application to
  a specific database.
• Six Steps to Using JDBC
• Load the Driver
• Establish the Database Connection
• Create a Statement Object
• Execute the Query
• Process the Result Set
• Close the Connection
• Make sure to wrap your JDBC calls within
  try/catch blocks.